Dirt Cones Research Articles

How dirt cones form on glaciers: Field observation, laboratory experiments, and modeling.

Dirt cones are meter-scale structures encountered at the surface of glaciers, which consist of ice cones covered by a thin layer of ashes, sand, or gravel, and which form naturally from an initial patch of debris. In this article, we report field observations of cone formation in the French Alps, laboratory-scale experiments reproducing these structures in a controlled environment, and two-dimensional discrete-element-method-finite-element-method numerical simulations coupling the grain mechanics and thermal effects. We show that cone formation originates from the insulating properties of the granular layer, which reduces ice melting underneath as compared to bare ice melting. This differential ablation deforms the ice surface and induces a quasistatic flow of grains that leads to a conic shape, as the thermal length become small compared to the structure size. The cone grows until it reaches a steady state in which the insulation provided by the dirt layer exactly compensates for the heat flux coming from the increased external surface of the structure. These results allowed us to identify the key physical mechanisms at play and to develop a model able to quantitatively reproduce the various field observations and experimental findings.

Sediments from cryoconite holes and dirt cones on the surface of Svalbard glaciers: main chemical and physicochemical properties

Sediments from cryoconite holes and dirt cones on the surface of Svalbard glaciers: main chemical and physicochemical properties

Proglacial landform assemblage in a rapidly retreating cirque glacier due to temperature increase since 1970, Fuegian Andes, Argentina

The general trend of glacial retreat since the Little Ice Age has shown an acceleration during the last decades in Southern Argentine and Chilean Patagonia. The Fuegian Andes climatic records report an irregular mean annual temperature increase since 1970, with acceleration from 2015, and the Chato Glacier, as other regional cirque glaciers, has undergone a rapid ice front retreat. A detailed mapping of the proglacial area of the Chato Glacier allowed the identification of a landform assemblage related to the glacier retreat during the last decades. In this paper morphological and sedimentological features of this peculiar landform assemblage, generated in an intense glacial ablation environment, are described and the causes of their origin are discussed. Among the most remarkable landforms annual moraines, hummocky moraines, esker-like landforms, flutes, kettle ponds, dirt cones, glacifluvial deposits, pronival ramparts and collapsed moraines are found. The multitemporal analysis of the Chato Glacier retreat allowed us to interpret that most of these landforms were generated when the landscape became ice-free after 2005. The Chato Glacier cirque floor gentle slope, the thin-ice thickness and the occurrence of a rocky threshold near the glacier front would have promoted the rapid glacier thinning and the disconnection of dead ice. This context, together with the sediments and meltwater availability, would have favored the development of this landform assemblage which is ephemeral due to its high susceptibility to erosion.

Water bears dominated cryoconite hole ecosystems: densities, habitat preferences and physiological adaptations of Tardigrada on an alpine glacier

We investigated the Forni Glacier and the surrounding area in the Alps in terms of habitat preferences, densities, dispersal and desiccation tolerance of glacier tardigrades, which are one of the most common faunal representatives and top consumers in supraglacial ecosystems. To do so, we sampled supraglacial environments (cryoconite holes, debris from ice surface, dirt cones and moraine, mosses from supraglacial stones) and non-glacial habitats (mosses, freshwater sediments and algae), and we installed air traps on the glacier and the nearby area. We found that cryoconite holes on the Forni Glacier are exclusively dominated by one metazoan group of tardigrades, representing one species, Hypsibius klebelsbergi (identified by morphological and molecular approaches). Tardigrades were found in 100% of cryoconite holes and wet supraglacial sediment samples and reached up to 172 ind./ml. Additionally, we found glacier tardigrades in debris from dirt cones and sparsely in supraglacial mosses. Glacier tardigrades were absent from freshwater and terrestrial samples collected from non-glacial habitats. Despite the fact that H. klebelsbergi is a typical aquatic species, we showed it withstands desiccation in sediments, but in low temperatures only. Treatments conducted in higher temperatures and water only showed low or no recovery. We suspect successful dispersal with wind might have taken place only when tardigrades desiccated in sediments and were passively transported by cold wind. Limited ability to withstand high temperatures and desiccation may be potential barriers preventing glacier tardigrades inhabiting new, even apparently suitable high mountain water bodies like temporary rock pools.

Potential sources of bacteria colonizing the cryoconite of an Alpine glacier.

We investigated the potential contribution of ice-marginal environments to the microbial communities of cryoconite holes, small depressions filled with meltwater that form on the surface of Forni Glacier (Italian Alps). Cryoconite holes are considered the most biologically active environments on glaciers. Bacteria can colonize these environments by short-range transport from ice-marginal environments or by long-range transport from distant areas. We used high throughput DNA sequencing to identify Operational Taxonomic Units (OTUs) present in cryoconite holes and three ice-marginal environments, the moraines, the glacier forefield, and a large (> 3 m high) ice-cored dirt cone occurring on the glacier surface. Bacterial communities of cryoconite holes were different from those of ice-marginal environments and hosted fewer OTUs. However, a network analysis revealed that the cryoconite holes shared more OTUs with the moraines and the dirt cone than with the glacier forefield. Ice-marginal environments may therefore act as sources of bacteria for cryoconite holes, but differences in environmental conditions limit the number of bacterial strains that may survive in them. At the same time, cryoconite holes host a few OTUs that were not found in any ice-marginal environment we sampled, thus suggesting that some bacterial populations are positively selected by the specific environmental conditions of the cryoconite holes.

Landform assemblage in Isidis Planitia, Mars: Evidence for a 3 Ga old polythermal ice sheet

The floor of Isidis Planitia, a giant impact basin located close to the martian equator, exhibits a landform assemblage, nicknamed Thumbprint Terrain, made of Arcuate Ridges, Aligned Cones, Isolated Cones, Cone Fields, associated with a peripheral network of Sinuous Ridges, Linear Depressions, and Mounds. From a new comprehensive mapping initiative of these landforms and from comparisons with terrestrial analogues (ribbed moraines, dirt cones, kettle holes, eskers, tunnel valleys and moraine plateaux), we demonstrate that this distinctive assemblage is a glacial landsystem inherited from the presence of a massive polythermal ice sheet over the basin during the Hesperian. The flow of the ice sheet was controlled by its basal thermal regime. Wet-based conditions led to the formation of Arcuate Ridges and Aligned Cones in most parts of the basin, while a negative geothermal anomaly due to impact-related crustal thinning was responsible for cold-based conditions in its central part, where only Isolated Cones and Cones Fields are present. Sinuous Ridges, Linear Depressions and Mounds at the basin margins are interpreted as relicts of a radial network of subglacial channels, which drained the glacial meltwater produced within the interior of the ice sheet across its cold-based periphery.

Geologic reconnaissance of Lautaro Volcano, Chilean Patagonia

Lautaro is the volcano closest to the Chile Triple Junction in the Andean Austral Volcanic Zone. The volcanic edifice of 3,607 m a.s.l. stands out on the north-western part of the plateau of the South Patagonian Ice Field. The volcano basement is composed of low-grade meta-pelites that are cut by tabular intrusive bodies of hornblende-biotite granite. The volcano is almost completely covered by ice and the study was performed on volcanic detritus present in terminal moraines of the Lautaro Glacier and the tephra on the surface of the O'Higgins Glacier. The terminal moraines of Lautaro Glacier contain fragments of light grey dacite rich in plagioclase and hornblende phenocrysts. Some dacite blocks show prismatic jointing, suggesting an origin of hot emplacement and subsequent rapid cooling, possibly resulted from collapse of a steep lava front. Some samples have glassy groundmass and rhyolite-like flow texture, with presence of mafic inclusions and bread crust bomb texture. The surface of the O'Higgins Glacier is covered by lapilli-size pumice fallout deposit. There are many dirt cones covered by volcanic ash composed of pumice fragments, volcanic glass, quartz, plagioclase, biotite, hornblende, and orthopyroxene. The ash and pumice are similar in chemical composition, both indicating an adakitic signature. At least three layers of fallout deposits have been recognised in parts of the surface of the glacier, which may correspond to the latest known eruptions.

Organic Contaminant Release from Melting Snow. 2. Influence of Snow Pack and Melt Characteristics

Large reservoirs of organic contaminants in seasonal snowpack can be released in short pulses during spring snowmelt, potentially impacting the receiving ecosystems. Laboratory experiments using artificial snow spiked with organic target substances were conducted to investigate the behavior of six organic contaminants with widely variable distribution properties in melting snow. Whereas the influence of a chemical's equilibrium phase partitioning on the elution behavior is explored in a companion paper, we discuss here the impact of snow properties and melt features, including the snowpack depth, the temperature at the interface between soil and snow, the meltwater content the internal ice surface area, and the existence of distinct snow layers. Water-soluble organic substances are released in high concentrations at the beginning of a melt period when a deep and aged snowpack undergoes intense melting. Warm ground can cause notable melting at the snow bottom leading to a delayed and dampened concentration peak. Hydraulic barriers in layered snow packs cause preferential meltwater flow which also mitigates the early contaminant flush. Hydrophobic organic pollutants that are associated with particles accumulate near the snow surface and are released at the end of melting. Dirt cones at the surface of a dense snowpack enhance this enrichment. The findings of this laboratory study will aid in the understanding of the behavior of organic pollutants during the melting of more complex, natural snow covers.

Debris transport in a temperate valley glacier: Haut Glacier d’Arolla, Valais, Switzerland

AbstractThis paper considers the role of structural glaciology in debris entrainment, transport and deposition at Haut Glacier d’Arolla, a temperate valley glacier in Valais, Switzerland. Sedimentological descriptions and cIast anaIysis have been used to identify reIationships between ice structure and debris transport. Relationships identified are (1) debris associated with crevasse traces, (2) the folding of rockfall material incorporated within primary stratification to form medial moraines and (3) dirt cones and engIaciaI debris Iayers associated with reactivated crevasse traces. A conceptuaI modeI is introduced to summarize the manner in which ice structures at Haut Glacier d’Arolla control entrainment and deposition of debris.

Circular moraine features on the Varanger Peninsula, northern Norway, and their possible relation to polythermal ice sheet coverage

This paper introduces a new hypothesis about the formation of circular moraine features (CMFs) on felsenmeer-covered plateaux of the Varanger Peninsula, northern Norway. CMFs and glacial lineations in the northwestern part of the Varanger Peninsula were mapped from aerial photographs. In two CMF-rich areas, Basečœrro-Plateau and Båtsfjordfjellet, the CMFs were investigated during fieldwork. The aim was to investigate possible entrainment, transport and deposition mechanisms of the CMFs in connection to ice sheet properties. The CMFs were deposited in connection with a polythermal ice cover. During glaciations, the ice sheet was cold-based on the boulder field plateaux and warm-based in valleys, especially in ice drainage pathways towards fjords. The CMF material was probably entrained en masse, on the Varanger Peninsula, in transition zones between warm- and cold-based ice. The debris transport took place close to the ice base. During deglaciation, the debris formed dirt cones, slowing down the melting of underlying dead-ice blocks. As material slid down the margins of the cones, the typical CMF shape was formed.

Theory of structure formation in snowfields motivated by penitentes, suncups, and dirt cones.

Penitentes and suncups are structures formed as snow melts, typically high in the mountains. When the snow is dirty, dirt cones and other structures can form instead. Building on previous field observations and experiments, this paper presents a theory of ablation morphologies, and the role of surface dirt in determining the structures formed. The glaciological literature indicates that sunlight, heating from air, and dirt all play a role in the formation of structure on an ablating snow surface. The present paper formulates a minimal model for the formation of ablation morphologies as a function of measurable parameters and considers the linear stability of this model. The dependence of ablation morphologies on weather conditions and initial dirt thickness is studied, focusing on the initial growth of perturbations away from a flat surface. We derive a single-parameter expression for the melting rate as a function of dirt thickness, which agrees well with a set of measurements by Driedger. An interesting result is the prediction of a dirt-induced traveling instability for a range of parameters.

Occurrence of dirt cones in Antarctica

Abstract Two types of dirt cone (sorted and unsorted) are recognised and described from moraine deposits on glaciers in some widely separated regions along the Transantarctic Mountains. It is suggested that dirt cone formation may have been more extensive in the past and that some of the older moraine deposits occurring in Antarctica may have formed by ablation in the manner described here.

A Quantitative Assessment of Dirt-Cone Dynamics

AbstractQuantitative investigations have been made of ice-cored dirt cones on Bersaerkerbræ in north-east Greenland. Experiments were also undertaken to evaluate field observations. Measurements included: maximum cone dimensions, sediment thickness and particle size, cone growth rates, slope angles and the temperature distribution within the debris layer and ice core. Particle size, which has not been stressed in previous studies, and related liquid consistency limits, appear as the dominant controls in cone formation, independent of debris thickness within the observed range of 10 mm to 125 mm. A threshold grain-size for dirt-cone inception was found, between 0.2 mm and 0.6 mm. The growth of cones was usually not more than 50% of the ablation over “clean” ice. Temperature measurements within dirt cones has enabled heat-flow studies to be made, evaluating the thermal conductivity of a sediment layer and the heat transfer involved in melting the ice core. A simple model of dirt-cone dynamics is proposed, characterized by negative feedbacks and describing a steady-state system.

A Quantitative Assessment of Dirt-Cone Dynamics

AbstractQuantitative investigations have been made of ice-cored dirt cones on Bersaerkerbræ in north-east Greenland. Experiments were also undertaken to evaluate field observations. Measurements included: maximum cone dimensions, sediment thickness and particle size, cone growth rates, slope angles and the temperature distribution within the debris layer and ice core. Particle size, which has not been stressed in previous studies, and related liquid consistency limits, appear as the dominant controls in cone formation, independent of debris thickness within the observed range of 10 mm to 125 mm. A threshold grain-size for dirt-cone inception was found, between 0.2 mm and 0.6 mm. The growth of cones was usually not more than 50% of the ablation over “clean” ice. Temperature measurements within dirt cones has enabled heat-flow studies to be made, evaluating the thermal conductivity of a sediment layer and the heat transfer involved in melting the ice core. A simple model of dirt-cone dynamics is proposed, characterized by negative feedbacks and describing a steady-state system.

Ablation Cones on Sidujökull, Iceland

The subject of this study is the ephemeral relief of the edge of one of the Vatnajokull outlet glaciers, called Sidujokull, developed in the shape of dirt cones. Special attention has been paid to the distribution of these forms, influenced by the existence of a system of fissures, supraglacial channels and shear planes in the glacier surface, and to the origin of covering material and development of conical forms. Taking into account the main process of ablation and the shape, a suggestion is made to use the term ‘ablation cone’ instead of ‘dirt cone’.

Lake Miers, South Victoria Land, Antarctica

Abstract The morphology, physics, and chemistry of Lake Miers (78° 07′ S, 163° 54′ E), a warm freshwater Antarctic lake, are discussed. The presence of rock debris on the floating lake ice has led to the formation of dirt cones and melt pools. Fossil levels of these pools show that the annual ablation is 15–20 cm. Despite a mean annual air temperature of − 20 ° c, the bottom waters of the lake are at + 5 ° C. This is shown to be a natural example of solar heat storage and the observed temperature profile is satisfactorily accounted for. Chemical evidence suggests that the lake has been filled by freshwater containing K, Na, Cl, and O2 , and that it is now stagnant below the 4° C depth. In this lower zone Ca, Mg, CO2, and SiO2 are diffusing upwards from the lake bed, possibly partly released by anaerobic biological activity.

Experiments on a Snow-Patch in the Mountains of Sweden

AbstractInvestigations into the mechanism of dirt-cone formation, and snow patterning, are described. In each case the changes in patches of various materials arranged on a snow surface, were observed over a period of three weeks in the summer, under varying weather conditions. The effects of fine rock flour on the formation of dirt cones are analysed. Two main weather types are recognized as having different, but important, effects on the surface features of the snow; föhn-type winds, and calm, sunny conditions.

Experiments on a Snow-Patch in the Mountains of Sweden

AbstractInvestigations into the mechanism of dirt-cone formation, and snow patterning, are described. In each case the changes in patches of various materials arranged on a snow surface, were observed over a period of three weeks in the summer, under varying weather conditions. The effects of fine rock flour on the formation of dirt cones are analysed. Two main weather types are recognized as having different, but important, effects on the surface features of the snow; föhn-type winds, and calm, sunny conditions.

The Recession of an Icelandic Glacier

THE accumulation OF quantitative data concerning rates of glacier recession in Iceland began in 1930, and figures relating to a few laciers have been made available.1 However, there is no such information for Hagafellsjokull Eystri and Hagafellsjokull Vestri, which are located at the south-eastern corner of Langjokull, nor, so far as is known, have Icelandic workers in this field made any measurements in that area. This paper constitutes an attempt to deduce, from an examination of maps and aerial photographs of different date, quantitative data relating to the reces? sion of Hagafellsjokull Eystri (E. Glacier) throughout the period 1934-56 and also during certain subdivisions thereof. A quantitative assessment is also made of the mean annual rate of lowering of the glacier surface during the interval 1950-6, and the resulting figure would seem to contribute to our knowledge of the life-history of dirt cones, at least in this particular area. The Hagavatn overflow-channels: Hagavatn (Fig. 1) is a typical ice-dammed marginal lake which came into existence when the building of Lambahraun, a post-glacial but pre-historic lava cone, blocked the drainage along an older north-east to south-west valley. The lake is dammed along its north-eastern side by the E. Glacier and it has at different times overflowed across the Jarlhettur range through four separate channels. A map prepared by the Icelandic cartographer Gunnlaugsson in the summers of 1834 and 1835 2 shows that Hagavatn, having abandoned its first outlet (Mosaskard),3 was at that time draining through channel 2 (Fagridalur). Since the heights of the four channel entrances decrease successively from south to north, flooding of the lowlands to the south will occur when the snout of the E. Glacier is receding, but not when it is advancing. Floods resulting from outpouring through channel 3 (Leynifoss) occurred in 1884,4 19024 and 1929.4' 5? 6? 7 Thus, prior to 1884, the snout of the E. Glacier must have been receding, but this phase must have been followed by a period of advance since subsequent recession resulted in another flood through channel 3 in 1902. Likewise, the glacier snout must have advanced again after 1902, otherwise recession could not have occasioned a third flood through channel 3 in 1929. By 1939 the glacier had further receded to such an extent that on August 13 of that year channel 4 was uncovered. Consequently, there was another disastrous flood over parts of the southern lowlands,8 and on this occasion the partial draining of the lake exposed a fine series of varves, particularly near the new south-eastern shore of Hagavatn. 9 The precise dating of the Hagavatn floods has, therefore, already made it possible to reach generalized conclusions concerning the fluctuations of the E. Glacier,4 but no quantitative data have hitherto been available. The recession of the E. glacier: a quantitative assessment: The Hagavatn area was mapped on a scale of 1 -.20,000 by the Cambridge University Expedition of 1934,10 and in August 1950 it was re-mapped on a scale of 1 '.25,000 by the Durham University Exploration Society.11 Vertical air photographs of the area taken on 23 September 1945, at a scale of approximately 1 -.45,000, were made available to the authors through the courtesy of Hr. Agust Bodvarsson of Landmaelingar Islands, Reykjavik. One of the tasks undertaken by the British Schools Exploring Society's 1956 Expedition to central Iceland was the re-mapping of the Hagavatn area on a scale of 1:25,ooo.12 It was hoped that by transferring to this map the positions of the E. Glacier snout in 1934, 1945 and 1950, it would be possible to present a quantitative assessment of the mean rate of recession of this glacier throughout the period 1934-56, as well as during the separate subdivisions thereof.

Studies of the Shrinkage After a Sudden Advance, Blue Bands and Wave Ogives on Glaciar Universidad (Central Chilean Andes)

AbstractThe recently discovered Glaciar Universidad is the second largest glacier in central Chile. Aerial photographs taken in 1945 show that just before that date it had undergone a “glacier flood” or sudden advance, similar to those suffered by four other great glaciers of central Chile between 1927 and 1947. The cause of these floods is sought. Surface features (firn line, absence ofpenitentesbut presence of “pocket-penitents”, glacier mills, dirt cones, water-filled holes with submerged ice crystals in them) prove that Glaciar Universidad is the most northerly glacier in the Andes of an Alpine type. The disposition of blue bands, crevasses, closed crevasses and shear planes is reported. Wave ogives are studied and an explanation is given of why dark Forbes’ bands form subsequently on these waves. A kind of unstratified esker of a form similar to a deposit observed by Mr. W. H. Ward in Baffin Island, has been studied, as also has the shearing of the frontal cliff along dirt strata; a theory of both phenomena according to which shear transfers material from the bed to the surface is questioned.